Exhaust emission control apparatus for internal combustion engine

ABSTRACT

To provide an exhaust gas purifying system for an internal combustion engine capable of executing an optimal regenerative operation by predicting a temperature of an absorbent based on running state information. 
     There are predicted the amount of nitrogen oxides (NO x ) to be absorbed by an absorbent 125 incorporated in a catalyst 124 and the temperature of the absorbent, based on the running state information obtained from a car navigation system 141 or traffic information service receiver 142, and the regenerative operation schedule is determined based on the prediction. Thus, the regenerative operation is conducted at the timing where NO x  has been duly absorbed by the absorbent and the absorbent temperature is lower than a predetermined temperature, so that the leakage of NO x  into the exterior of a vehicle can be restrained.

TECHNICAL FIELD

The present invention relates to an exhaust gas purifying system for aninternal combustion engine or, more particularly, to an exhaust gaspurifying system for an internal combustion engine in which a poisonousgas component in the exhaust gas is trapped, stored and periodicallyremoved.

BACKGROUND ART

Various types of exhaust gas purifying systems, for purifying theexhaust gas emitted from an internal combustion engine, are usedaccording to the properties of the exhaust gas, and many of them trap apoisonous component contained in the exhaust gas and requireregeneration operation at appropriate time intervals.

For example, an exhaust gas purifying system, for a gasoline engine or,especially, for a gasoline engine which executes lean burning for mostof the running period, except accelerating periods or the like, whichabsorbs nitrogen oxide for the lean burning period and releases theabsorbed nitrogen oxide for the short rich burning period has alreadyproposed (Refer to International Publication No. W093/07363).

The above-mentioned exhaust purifying system absorbs nitrogen oxidecontained in the exhaust gas in an absorbent incorporated in the exhaustgas purifying system for the lean burning period, which accounts formost of the running period, and executes a regeneration operation whichreleases the nitrogen oxide from the absorbent by increasing an amountof fuel to make air-fuel ratio rich when it is determined that theabsorbing power has deteriorated. Note, nitrogen oxide released duringthe regeneration operation is not directly emitted into the air becauseit is deoxidized by unburned hydrocarbon and carbon monoxide andconverted to nitrogen gas, carbon dioxide and water in the exhaust gaswith rich air-fuel ratio. The nitrogen oxide released for theregeneration operation is dioxidized by unburned hydrocarbon in theexhaust gas, the air-fuel ratio thereof being rich, and thus isconverted into nitrogen gas, carbon dioxide and water. The nitrogenoxide, therefore, is not emitted into the air.

However, if the remaining absorbing power of the absorbent is evaluatedbased on the integrated value of the product of the intake air flow ratewhich is proportional to the amount of nitrogen dioxide in the exhaustgas and the engine load or in a more simplistic manner, based on theintegrated value of the engine speed, and a regeneration operation isexecuted when it is determined that the remaining absorbing powerdecreases below a fixed level, it is not avoidable that the nitrogenoxide is emitted in the air depending on the exhaust gas temperature.

Because the air-fuel ratio in the absorbent gradually changes from thelean state to the rich state when the air-fuel ratio is controlled fromthe lean state to the rich state, nitrogen oxide is not completelydeoxidized and is liable to be emitted in the air before the actualair-fuel ratio has been completely transferred to the rich state.

However, it is known that the discharge amount of nitrogen oxide whenswitching the air-fuel ratio from rich to lean depends mainly on thetemperature of the absorbent and becomes almost zero when thetemperature of the absorbent is lower than 200° C.

Therefore, the present applicant has already proposed stopping theregeneration operation as long as the absorbent has a residualabsorption power when the temperature of the absorbent (or the exhaustgas) rises over the temperature where the regeneration operation ispermitted.

However, the regeneration operation of the exhaust gas purifying systembased on the current temperature of the absorbent is not always optimal.

Namely, even if the regeneration timing of the exhaust gas purifyingsystem is controlled based on the current temperature of the exhaust gasin addition to the integrated value of the engine speed, the nitrogenoxide is liable to be emitted into the air when the exhaust gastemperature suddenly rises while the exhaust gas purifying system isregeneration, and when the exhaust gas temperature becomes thetemperature where regeneration operation is permitted while the nitrogenoxide is being absorbed, the fuel consumption may unnecessarily increaseto enrich the air-fuel ratio.

On the other hand, in an exhaust gas purifying system for a dieselengine, the particulate filter thereof, for trapping particulates(carbon particles) contained in the exhaust gas, is periodicallyregenerated as has been proposed (Japanese Unexamined Patent Publication(Kokai) No. 1-318715).

Namely, for the diesel engine, a particulate filter is installed in theexhaust system in order to remove the particulates from the exhaust gasbefore the gas is emitted into the atmosphere. Because the trappingpower of the particulate filter is limited, it is necessary to removethe particulate at appropriate times.

Therefore, the above described exhaust gas purifying system proposes notonly to promote the spontaneous burning off of the particulates byadding catalyst in the particulate filter, but also the burning-off ofthe particulates by continuing the reaction between the particulates andthe nitrogen dioxide which is converted from nitrogen monoxide, by anoxidation catalyst installed upstream of the particulate filter, whenthe exhaust gas temperature is not so high.

Because conversion of nitrogen monoxide into nitrogen dioxide by theoxidation catalyst, however, requires that the exhaust gas temperatureis within a predetermined range, the particulates cannot be burned offwhen the exhaust gas temperature is out of the predetermined range.

Therefore, it has been proposed to promote the burning off of theparticulates by raising the exhaust gas temperature into thepredetermined temperature range, by heating with a light oil burner oran electric heater, by closing the intake air, or by combining theabove, when it is determined that the exhaust gas temperature is out ofthe predetermined range based on the rotational speed and the load ofthe diesel engine.

Nevertheless, when the exhaust gas temperature shifts into thepredetermined range and it becomes possible to remove the particulatewithout heating by the light oil burner or the like after it isdetermined that the heating with the light oil burner or the like isnecessary because the exhaust gas temperature is out of thepredetermined range, the fuel consumption rate is unavoidablydeteriorated due to the unnecessary heating.

DISCLOSURE OF THE INVENTION

Accordingly, the object of the present invention is to provide anexhaust gas purifying system, for an internal combustion engine, whichcan optimally execute a regeneration operation without deteriorating thefuel consumption rate by predicting a future state of the exhaust gasaccording to an information fetched from a navigation system or thelike.

According to this invention, there is provided an exhaust gas purifyingsystem comprising a trapping means for trapping a poisonous componentcontained in the exhaust gas emitted from an internal combustion engine,a removing means for removing the poisonous component trapped by saidtrapping means from the trapping means, an exhaust gas state predictingmeans for predicting a future state of the exhaust gas emitted from theinternal combustion engine, a regeneration timing determining means fordetermining a regeneration timing to regenerate said trapping meansusing said removal means based on the state of the exhaust gas predictedby said exhaust gas state predicting means, and a regeneration executingmeans for executing the regeneration of said trapping means by saidremoval means at the regeneration timing determined by said regenerationtiming determining means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of an embodiment of an exhaust gaspurifying system for a gasoline engine according to the presentinvention.

FIG. 2 is a flowchart of a scheduling routine for an exhaust gaspurifying system for a gasoline engine.

FIG. 3 is a flowchart of a regeneration operation timing determiningroutine.

FIG. 4 is a flowchart of a regeneration operation routine.

FIG. 5 is a flowchart of a regeneration execution routine.

FIG. 6 is a flowchart of a fuel injection routine.

FIG. 7 is a diagram for explaining the effects of the invention.

FIG. 8 is a configuration diagram showing an embodiment of an exhaustgas purifying system for a diesel engine according to the invention.

FIG. 9 is a diagram showing an operating area for removing particulates.

FIG. 10 is a flowchart of a scheduling routine for an exhaust gaspurifying system of a diesel engine.

FIG. 11 is a flowchart of a second regeneration operation schedulingroutine.

FIG. 12 is a flowchart of a second regeneration execution routine.

FIG. 13 is a diagram for explaining the effects in the case where theexhaust gas purifying system is a particulate filter.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a configuration diagram according to the present inventionapplied to a gasoline engine.

For the gasoline engine 10, intake air is supplied through an aircleaner 111, an intake pipe 112, a surge tank 113, a branch pipe 114 andan intake valve 115.

A throttle valve 116 is mounted in the intake pipe 112 to control theamount of the intake air supplied to the gasoline engine 10. Also, afuel injection valve 117 is installed in the branch pipe 114 to injectthe fuel into the intake air.

The mixture supplied to a combustion chamber 101 is compressed by therising of a piston 102 while the piston 102 is moving up, and ignited bya spark plug 103 to be burned near the top dead center so that thepiston 102 is moved down to generate driving power.

After burning, the exhaust gas is supplied to an exhaust gas purifyingunit 124, through an exhaust valve 121, an exhaust manifold 122 and anexhaust pipe 123, so that it is purified in the purifying unit 124.

The exhaust gas purifying unit 124 contains nitrogen oxide absorbent125. When the amount of residual oxygen is small in the exhaust gas, thenitrogen oxide is absorbed, while when the amount of residual oxygen inthe exhaust gas is large, the nitrogen oxide absorbed is released.

This exhaust gas purifying unit 124 is controlled by a control unit 13which is a microcomputer system. The control unit 13 consists of notonly a bus 131 but also a CPU 132, a memory 133, an input interface 134and an output interface 135.

To the input interface 134, a throttle opening sensor 137 which detectsthe opening of the throttle valve 116, an intake air pressure sensor 137which detects the pressure in the surge tank 113, a crank angle sensor138 which detects the rotational speed of the gasoline engine 19 and anabsorbent temperature sensor 139 which detects the temperature of theabsorbent 125 contained in the exhaust gas purifying unit 124 areconnected.

Further, at least one of a car navigation system 141 and a vehicleinformation and communication system receiver 142 is also connected tothe input interface, and the information on running conditions obtainedfrom the car navigation system 141 and the vehicle information andcommunication system receiver 142 is fetched into the control unit 133.

To the output interface 135, the spark plug 103 and the fuel injectionvalve 117 are connected and controlled by an ignition command and a fuelinjection valve opening command output from the control unit 13.

FIG. 2 is a flowchart of a scheduling routine executed in the controlunit 13 before the vehicle begins running, and information on the routefound by the car-navigation system 141, such as a running distance, aroad type (express road or normal road), a running height, etc., isfetched at step 21.

A traffic congestion forecast, traffic control information, etc.received by the vehicle information and communication system receiver142 are fetched at step 22.

At step 23, the route to the destination is divided into i_(max)sections according to the information and the traffic congestionforecast, and then a running distance D(i), a running speed S(i), a loadof the gasoline engine L(i), an amount of generated nitrogen oxide C(i),a temperature of the absorbent T(i), etc. are predicted for each runningsection i (1≦i≦i_(max)).

At step 24, in order to determine the regeneration timing of the exhaustgas purifying system for all running sections, a running section indexi_(s) is set to "1" as the initial value, and the regeneration operationscheduling routine for the exhaust gas purifying system is executed atstep 25 to terminate the routine.

FIG. 3 is a flowchart of the regeneration operation timing determiningroutine executed at step 25. The amount of nitrogen oxide C(i_(s))predicted to be generated in the running section "i_(s) " is added tothe amount of nitrogen oxide Q absorbed by the exhaust gas purifyingsystem often running in the preceding running section to determine theamount of nitrogen oxide Q absorbed by the exhaust gas purifying systemafter running in the running section "i_(s) ".

It is determined whether or not the amount of nitrogen oxide Q afterrunning through section "i_(s) " is larger than a minimum absorptionamount Q_(min) (for example, 10%).

When the determination at step 252 is negative, that is, when it isdetermined that nitrogen oxide is not absorbed in the exhaust gaspurifying system, the control proceeds to step 253 where theregeneration operation flag R(i_(s)) for the running section "i_(s) " isset to "0" because the regeneration operation is not required for therunning section "i_(s) ".

When the determination at step 252 is affirmative, that is, when it isdetermined that nitrogen oxide is absorbed in the exhaust gas purifyingsystem, the control proceeds to step 254 where it is determined whetheror not the absorbent temperature T(i_(s)) for the running section "i_(s)" is lower than the temperature where the regeneration operation ispermitted T_(allow).

The reason why the determination is done is that nitrogen oxide isliable to be emitted into the air by the regeneration operation when theabsorbent temperature rises above the temperature, where theregeneration operation is permitted, T_(allow) though it is necessarythat the absorbent temperature is higher than the activationtemperature, as described above.

When the determination at step 254 is negative because it is predictedthat the absorbent temperature T(i_(s)) for the running section is overthe temperature where the regeneration operation is permitted, thecontrol proceeds to step 255 where it is determined whether or not theamount of nitrogen oxide absorbed after running in the running section"i_(s) " is larger than a maximum absorption amount Q_(max) (forexample, 70%).

When the determination at step 255 is negative, that is, when theabsorption power has a margin, the control proceeds to step 253 as theregeneration operation is not performed.

When the determination at step 255 is affirmative, that is, when theamount of nitrogen oxide Q after completing running the running section"i_(s) " exceeds the maximum absorption amount Q_(max), and when thedetermination at step 254 is affirmative, that is, when the regenerationoperation is permitted for the running section "i_(s) ", then thecontrol proceeds to step 256 for setting the regeneration operation flagR(i_(s)) to "1" for the running section "i_(s) " and resetting theamount of nitrogen oxide Q.

After completing processing at steps 253 and 256, it is determinedwhether or not the running section index i_(s) has reached the maximumvalue i_(max) at step 257, and the control returns to step 251 after thesection index is incremented at step 285 when the determination at step257 is negative. Note, when the determination at step 257 isaffirmative, this routine is directly terminated.

FIG. 4 is a flowchart of the regeneration operation routine executedafter the vehicle begins running, and this routine is executed as aninterrupt routine every predetermined time interval.

The actual running distance after the vehicle begins running D_(r) isread out, for example, from the trip meter at step 41 and it isdetermined whether or not the actual running distance is larger than thepredicted running distance D_(s) (i_(t)) up to the section it. Note, therunning section i_(t) and the predicted running distance D_(s) are setto "0" in the initialization routine which is not shown.

When the determination at step 42 is affirmative, that is, when therunning section i_(t) has been completely covered, the control proceedto step 44 after the predicted distance D_(s) is renewed with followingequation and the section index i_(t) is incremented at step 43.

    D.sub.s ←D.sub.s +D(i.sub.t)

    i.sub.t ←i.sub.t +1

Note, when the determination at step 42 is negative, the controlproceeds directly to step 44.

It is determined that whether or not the regeneration execution flagR(i_(t)) for the running section i_(t) is "1" at step 44. When thedetermination at step 44 is negative, that is, when the vehicle isrunning in the running section for which the regeneration operation isnot executed, the control proceeds to step 48 after the air-fuel ratiocorrection coefficient K is set to a value K_(L) less than "1.0" (forexample, "0.7") in order to execute the lean burning, and the burningstate flag XF is set to "0" which indicates that the lean burning isexecuting.

When the determination at step 44 is affirmative, that is, when thevehicle is running in the section for which the regeneration operationis performed, the control proceeds to step 48 after the regenerationoperation is executed at step 47.

It is determined whether or not the vehicle is moving in accordance withthe predicted schedule.

This determination can be done by determining whether or not the actualvalues of the speed, the gasoline engine load (for example, the intakemanifold pressure) and the absorbent temperature agree with thecorresponding predicted values within the predetermined limits.

When the determination at step 48 is negative, that is, when the vehicledoes not run according to schedule, the routine is terminated after thescheduling routine shown in FIG. 3 is again executed at step 49. Whenthe determination at step 48 is affirmative, that is, when the vehicleruns according to schedule, this routine is directly terminated.

FIG. 5 is a flowchart of a regeneration executing routine executed instep 47. It is determined whether or not the burning state flag XF is"0" at step 471.

When the determination at step 471 is affirmative, that is, when theburning has been under the lean state, the routine is terminated afterthe air-fuel ratio correction coefficient K is set to a value K_(R)larger than "1.0" (for example, "1.3") at step 472, and the burningstate flag XF is set to "1" which indicates that the rich burning isexecuting.

When the determination at step 471 is negative, that is, theregeneration operation has already begun, it is determined whether ornot the period required for the regeneration operation has elapsed atstep 474. When the determination is negative, the control proceeds tostep 472, while when the determination is affirmative, the controlproceeds to step 475.

That is, when the regeneration operation is regarded as being completed,this routine is terminated after the air-fuel ratio correctioncoefficient K is set to K_(L) to restore the burning state to the leanburning at step 475, and the burning state flag XF is set to "0" whichindicates that the lean burning is executing at step 476.

FIG. 6 is a flowchart of a fuel injection routine for determining theamount of fuel injected from the fuel injection valve 117, that is, theopening time of the fuel injection valve 117, and the rotational speedNe of the gasoline engine and the intake pipe pressure PM are fetched atstep 61.

The basic fuel injecting period TP is calculated as a function of therotational speed Ne of the gasoline engine and the intake manifoldpressure PM.

    TP←TP (Ne, PM)

Note, the basic fuel injecting period TP is determined as the openingperiod of the fuel injection valve for supplying the amount of fuelrequired for burning at the stoichiometric air-fuel ratio.

At step 63, the basic fuel injecting period TP is multiplied by theair-fuel ratio correction coefficient K to calculate the fuel injectingperiod TAU.

    TAU←K·TP

Consequently, as long as the air-fuel ratio correction coefficient K isset to K_(L), the gasoline engine is in a lean burning state, while aslong as it is set to K_(R), the gasoline engine is in a rich burningstate.

FIG. 7 is a diagram for explaining the effects of the present inventionwhen it is applied to the gasoline engine. The abscissa denotes thetime.

(a) shows the information of the route and the traffic congestionforecast obtained from the car navigation system 141 and the vehicleinformation and communication system receiver 142 and the vehicle speedpredicted based on the above information.

(b) shows the load of the gasoline engine, the absorbent temperature andthe concentration of nitrogen oxide predicted by the control unit 13.

(c) shows the amount of the nitrogen oxide absorbed in the absorbent andthe amount of the nitrogen oxide released from the absorbent predictedby the control unit 13.

Namely, the regeneration operation is postponed in the exhaust gaspurifying system until the absorbent temperature moves into thetemperature range where nitrogen oxide can never be emitted as long asthe absorbent retains its absorbing power while the absorbenttemperature is in the temperature range where nitrogen oxide may beemitted when it is determined that the amount of nitrogen oxide absorbedin the absorbent becomes a maximum.

(d) shows the regeneration operation performed by the conventionalexhaust gas purifying system of the gasoline engine. Namely, when it isdetermined that the amount of the nitrogen oxide absorbed in theabsorbent becomes a maximum, the regeneration operation is carried outregardless of the absorbent temperature. When the absorbent temperatureis high, therefore, nitrogen oxide is unavoidably emitted into the air.

Therefore, in the exhaust purifying system of the gasoline engineaccording to the present invention, not only the number of regenerationoperations is reduced but also the emission of the nitrogen oxide fromthe vehicle is suppressed.

FIG. 8 is a configuration diagram of an embodiment when the presentinvention is applied to a diesel engine. Numeral 81 designates a dieselengine, numeral 82 an intake manifold, numeral 83 an intake duct coupledto the confluence of the intake manifold 82, numeral 84 a throttle valvearranged in the intake duct 83, numeral 85 an actuator for driving thethrottle valve 84, numeral 86 an exhaust manifold, numeral 87 an exhaustpipe, numeral 88 a light oil supply unit, numeral 89 a casing forhousing an electric heater 810, numeral 811 a catalyst converter whichcontains oxidization catalyst 812, numeral 813 a filter casing whichcontains a honeycomb particulate filter 814, and numeral 815 an exhaustpipe. The light oil supply unit 88 is connected to a light oil supplypump 816 and a secondary air supply pump 817 driven by the dieselengine, and the light oil and the secondary air are supplied into theexhaust pipe 87 from the light oil supply unit 88 if necessary. Theelectric heater 810 can alternatively be installed in the oxidizationcatalyst 812.

The control unit 830 is a microcomputer system including a memory 832, aCPU 833, an input port 834 and an output port 835 interconnected by abus 831. A differential pressure sensor 818 for generating a signalproportional to the pressure difference between the upstream side andthe downstream side of the particulate filter 814 is installed on theparticulate filter 814, and the differential pressure sensor 818 isconnected to the input port 834. Further, a pair of temperature sensors819, 820 are installed for detecting the exhaust gas temperature on theupstream and downstream sides, and these temperature sensors 819, 820are also connected to the input port 834.

Also, the accelerator pedal 821 is equipped with a load sensor 822 forgenerating a signal proportional to the amount of depression of theaccelerator pedal 821, and the load sensor 822 is connected to the inputinterface 834. Further, an engine speed sensor 823 for outputting pulsesindicating the rotational speed Ne of the internal combustion engine isalso connected to the input sensor.

On the other hand, the actuator 85, the light oil supply unit 88, theelectric heater 810 and the secondary air supply pump 817 are connectedto the output port 835.

Further, in order to fetch the information of the vehicle operatingcondition, the car navigation system 841 and the vehicle information andcommunication system receiver 842 are connected to the input port 834.

Because the oxidization catalyst 812 has the absorbent, if the exhaustgas contains a large amount of nitrogen monoxide in the diesel engine orthe like, the nitrogen monoxide contained in the exhaust gas is absorbedwhen the temperature of the exhaust gas is low, while the nitrogendioxide absorbed in the nitrogen oxide absorbent is released when thetemperature of the exhaust gas is comparatively high.

Therefore, it becomes possible to remove the particulates caught in theparticulate filter 814 which is arranged at the downstream side of theengine with the nitrogen dioxide released from the oxidization catalystwhen the temperature of the exhaust gas is relatively high though it isnot enough high to cause spontaneous firing.

The operation of the exhaust gas purifying system shown in FIG. 9 willbe described below. The throttle valve 84 is fully open and the lightsupply unit 88 and the electric heater 810 are stopped under the normaloperating condition.

FIG. 9 is a diagram for explaining the operating zone for removing theparticulates. The ordinate denotes the engine load, and the abscissa theengine speed.

The conversion rate from nitrogen monoxide to nitrogen dioxide in theoxidization catalyst 812 increases when the exhaust gas temperature Tgis in the range of about 230° C. to 450° C., that is, when the operatingzone is "3". In this operating area, the particulates react with thenitrogen dioxide and are removed by burning without forcibly raising theexhaust gas temperature by the light burner 88 or the like.

When the operating condition belongs to the operating zone "5", theparticulates burn spontaneously without reaction with nitrogen dioxide.

Conversely in the operating zones "1" or "2", both the conversion ratefrom nitrogen monoxide to nitrogen dioxide and the exhaust gastemperature are so low that the particulates cannot be removed byburning.

Further, in the operating zone "4", the conversion rate from nitrogenmonoxide to nitrogen dioxide is low and the exhaust gas temperature isnot so high that the particulates burns spontaneously.

In the operating zone "4", therefore, it is possible to burn and removethe particulates by slightly closing the throttle valve 84 to raise theexhaust gas temperature.

In the operating zone "2", the particulates can be removed by raisingthe exhaust gas temperature with the electric heater 810 or by slightlyclosing the throttle valve 84.

Further, in the operating zone "1", the particulates can be removed byburning light oil, using the electric heater 810 and the light oilsupply unit 88, to raise the exhaust gas temperature.

That is, in the operating zones "3" or "5", it is possible to performthe regeneration operation for the particulate filter 814 withoutdeteriorating the fuel consumption rate, whereas the regenerationoperation for the particulate filter 814 in the remaining operatingzones deteriorates the fuel consumption rate due the use of the electricheater 10, the light oil supply unit 88 or the closing of the throttlevalve 84.

Therefore, it is necessary to make a schedule to perform theregeneration of the particulate filter 814 in the operating zones "3" or"5".

FIG. 10 is a flowchart of a second scheduling routine executed by thecontrol unit 13 before the vehicle begins running, and the informationof the route searched by the car-navigation system 841, such astraveling distance, road type (whether express road or normal road),altitude, etc., is fetched at step 101.

The traffic congestion forecast, traffic control information, etc.received by the vehicle information and communication system receiver842 at step 102.

At step 103, the route to the destination are divided into i_(max)sections according to the information and the traffic congestionforecast, and then a traveling distance D(i), a running speed S(i), aload of the diesel engine L(i), an amount of generated particulate C(i),a temperature of the exhaust gas Tg(i), etc. are predicted for eachsection i (1≦i≦i_(max)).

At step 104, in order to determine the regeneration timing of theexhaust gas purifying system for all sections, a section index i_(s) isset to "1" as the initial value, and the regeneration scheduling routinefor the particulate filter is executed at step 105 to terminate theroutine.

FIG. 11 is a flowchart of a particulate filter regeneration schedulingroutine executed at step 105. At step 105a, the amount of particulateC(i_(s)) generated while the vehicle is running in the current section"i_(s) " is added to the amount of particulate S trapped by theparticulate filter 814 after the vehicle has completed running at theprevious section to determine the amount of particulate S trapped whenthe vehicle has completed running at the section "i_(s) ", and theoperating zone of the section "i_(s) " is determined at step 105b.

When it is determined that the operating zone of the running section"i_(s) " is "1" or "2" at step 105b, the control proceeds to step 105cwhere it is determined whether or not the trapped amount of particulateS is larger than the maximum amount S_(max) (for example, 120%).

When the determination at step 105c is negative, that is, when theparticulate filter 814 has a margin of trapping power, the regenerationoperation flag R(i_(s)) for the section "i_(s) " is set to "0" whichindicates that any regeneration operations such as burning of the lightoil, heating with the electric heater or closing of the throttle valveare not performed.

When the determination at step 105c is affirmative, that is, when theparticulate filter 814 has no margin of trapping power, it isdeterminated whether or not the operating zone corresponding to thesection "i_(s) " is "1" or "2". If the operating zone is "1", theregeneration operation flag R(i_(s)) is set to "3" which indicates thatthe heating by burning of light oil and the heating by the electricheater are used at the same time at step 105f. When the operating zoneis "2", on the other hand, the regeneration operation flag R(i_(s)) isset to "2" which indicates that the heating by the electric heater andclosing of the throttle valve are used at the same time.

When the determination at step 105b is that the operating zone for thesection "i_(s) " is "3" or "5", the control proceeds to step 105h wherethe regeneration operation flag R(i_(s)) for section "i_(s) " is set to"0" because the particulates can be removed without a regenerationoperation.

When the determination at step 105b is that the operating zone for thesection is "4", the control proceeds to step 105i where it is determinedwhether or not the trapped amount of particulate S is larger than amiddle amount S_(mid) (for example, 100%).

When the determination at step 105i is affirmative, that is, when thetrapped amount of particulate S is not less than the middle amountS_(mid), the regeneration operation of the particulate filter 814 ispossible without deteriorating the fuel consumption rate in theoperating zone "4". In order to perform the regeneration operationbeforehand, the regeneration operation flag R(i_(s)) is set to "1" whichindicates that the throttle valve is slightly throttled.

When the determination at step 105i is negative, that is, when thetrapped amount of particulate S is less than the middle amount S_(mid),the regeneration operation flag R(i_(s)) for the section "i_(s) " is setto "0" which indicates that the regeneration operation is not performedbecause the particulate filter 814 has a margin of trapping power.

After completing the processing at steps 105f, 105g, 105h and 105i, thecontrol proceeds to step 105m after the amount of trapped particulates Sis reset at step 105l.

After completing the processing at steps 105d and 105k, the controlproceeds directly to step 105m without resetting the amount of trappedparticulate S because the regeneration operation of the particulatefilter is not performed.

It is determined whether or not the prediction for all sections at step105m, that is, whether or not the section index "i_(s) " has reached themaximum value i_(max).

When the determination at step 105m is negative, the control returns tostep 105a after the section index "i_(s) " is incremented at step105_(n). When the determination at step 105m is affirmative, incontrast, this routine is directly terminated.

FIG. 12 is a flowchart of a second regeneration operation routineexecuted after the vehicle begins running. This routine is executed asan interrupt routine every predetermined interval.

The actual traveling distance after the vehicle begins running is readout, for example, from the trip meter at step 120, and it is determinedthat the actual traveling distance is larger than the predictedtraveling distance D_(s) (i_(t)) up to the section i_(t). The sectioni_(t) and the predicted distance D_(s) are assumed to be set to "0" inthe initialization routine which not shown.

When the determination at step 121 is affirmative, that is, when thesection i_(t) has been completely covered, the control proceeds to step123 after the predicted distance D_(s) is renewed with the followingequation and the section index i_(t) is incremented at step 122.

    D.sub.s ←D.sub.s +D(i.sub.t)

    i.sub.t ←i.sub.t +1

Note, when the determination at step 121 is negative, the controlproceeds directly to step 123.

It is determined whether or not the regeneration execution flag R(i_(t))is "0" at step 123 and, when the determination is affirmative, thecontrol proceeds to step 128 without executing any process.

When the determination at step 123 is negative, the control proceeds tostep 124 for judging the value of the regeneration execution flagR(i_(t)).

When it is determined that the value of the regeneration execution flagR(i_(t)) is "1" at step 124, the control proceeds to step 128 afterslightly closing the throttle valve 84 at step 125.

When it is determined that the value of the regeneration execution flagR(i_(t)) is "2" at step 124, the control proceeds to step 128 forslightly closing the throttle valve 84 and activating the electricheater 810 at step 126.

When it is determined that the value of the regeneration execution flagR(i_(t)) is "3" at step 124, the control proceeds to step 128 after theelectric heater 810 is activated and light oil is supplied to theexhaust pipe 87 from the light oil supply unit 88 at step 127.

At step 128, it is determined whether or not the vehicle is being drivenin accordance with the schedule calculated in the regenerationscheduling routine.

This determination can be done by determining whether or not the actualvalues of the speed, the diesel engine load (for example the depressedamount of the accelerator pedal) or the exhaust gas temperature agreewith the predicted values of the speed, the diesel engine load or theexhaust gas temperature, and within the predetermined limits.

When the determination at step 128 is affirmative, that is, when thevehicle is driven in accordance with the schedule, this routine isdirectly terminated.

When the determination at step 128 is negative, that is, when thevehicle is not driven in accordance with the schedule, this routine isterminated after the regeneration operation is rescheduled at step 129.

The regeneration operation can be rescheduled by re-executing thescheduling routine shown in FIG. 11.

FIG. 13 is a diagram for explaining the effects of the invention appliedto the particulate filter of the diesel engine. The abscissa representsthe time, and the ordinates represent the predicted engine load, thepredicted exhaust gas temperature (solid line) and the predicted amountof generated particulates, the amount of trapped particulates and thedeteriorating degree of fuel consumption rate.

In respect of the amount of trapped particulates and the deterioratingdegree of fuel consumption rate, the solid line indicates when thepresent invention is applied and the dashed line indicates when theprior art is applied.

Specifically, according as the predicted engine load changes as"2"→"1"→"4"→"5", the predicted exhaust gas temperature and the predictedamount of generated particulates also change. The numerals in thepredicted engine load indicate the operating zone of FIG. 9.

When no regeneration operation is scheduled, as in the prior art, it isnecessary to burn off particulates by closing the throttle valve 94 toraise the temperature of the exhaust gas, because the amount ofparticulates trapped by the particulate filter reach 100% when thepredicted engine load is "4". In this case, the fuel consumption rate isdeteriorated as the result of closing the throttle valve 94.

Conversely, when the present invention is applied, the regenerationoperation is not executed because the particulate filter has a marginagainst the maximum trapping power, for example, 120%, even though theamount of trapped particulates reaches 100% when the predicted engineload is "4".

At the next section, the operating zone becomes "5" and the particulateis naturally burned off because the exhaust gas temperature becomeshigh. In this case, the throttle valve 94 is not closed, and thereforethe fuel consumption rate is not deteriorated.

What is claimed is:
 1. An exhaust gas purifying system for an internalcombustion engine, comprising:means for trapping polluting components ofexhaust gas emitted from the internal combustion engine; means forregenerating the trapping means by removing the polluting componentstrapped in the trapping means; means for predicting a future runningcondition of a vehicle in which the engine is mounted; means forpredicting a property of the exhaust gas based on the predicted futurerunning condition; means for determining a timing at which the trappingmeans should be regenerated by the removal means in accordance with thepredicted exhaust gas property; and means for executing regenerating ofthe trapping means by the removing means at the timing determined by theregeneration timing determining means.
 2. An exhaust gas purifyingsystem according to claim 1, wherein:the exhaust gas property predictingmeans is an exhaust gas temperature predicting means for predicting thetemperature of the exhaust gas emitted from said internal combustionengine based on the vehicle running condition predicted by said runningcondition predicting means.
 3. An exhaust gas purifying system accordingto claim 2, wherein:the trapping means is a catalyst for trappingnitrogen oxide in the exhaust gas when the exhaust gas is in a leanstate: the removing means enriches the exhaust gas to regenerate thecatalyst by releasing nitrogen oxide trapped in the catalyst; theregeneration timing determining means determines the regeneration timingof the catalyst based on the predicted future exhaust gas temperature;and the regeneration executing means enriches the exhaust gas at theenriching timing determined by the enriching timing determining means.4. An exhaust gas purifying system according to claim 3, wherein theenriching timing determining means determines the regeneration timing tocoincide with a time point at which the exhaust gas property predictingmeans reaches a predetermined regeneration threshold.
 5. An exhaust gaspurifying system according to claim 3, wherein the enriching timingdetermining means determines the enriching timing determining meansdetermines the regeneration timing to coincide with a time point atwhich the exhaust gas property predicting means is lower than apredetermined regeneration threshold.
 6. An exhaust gas purifying systemaccording to claim 1, whereinthe trapping means is a particulate filterfor trapping particulate emitted from the internal combustion engine;the removing means regenerates the particulate filter by burning offparticulate trapped therein; the regeneration timing determining meansdetermines the regeneration timing based on the predicted future exhaustgas property; and the regeneration executing means executes regenerationof the particulate filter at the particulate filter regenerating timingdetermined by the regenerating timing determining means.
 7. An exhaustgas purifying system according to claim 6, wherein the exhaust gasproperty predicting means predicts a temperature of the exhaust gasbased the predicted running condition.
 8. An exhaust gas purifyingsystem according to claim 7, wherein the regeneration timing determinedby the regeneration timing determining means determines is a time atwhich the predicted exhaust gas temperature is lower than apredetermined regeneration threshold.
 9. An exhaust gas purifying systemaccording to claim 6, wherein the regeneration timing determined by theregeneration timing determining means determines is a time at which thepredicted exhaust gas property reaches a predetermined regenerationthreshold.
 10. An exhaust gas purifying system according to claim 6,wherein the particulate filter regenerating means is at least one of ameans for slightly closing a throttle valve of the engine, an electricheater for heating the exhaust gas and means for burning fuel in theexhaust gas to heat the exhaust gas.
 11. An exhaust gas purifying systemaccording to claim 6, wherein:the particulate filter contains a catalystfor naturally burning off particulate; and when the exhaust gastemperature is higher than about 600° C., the regeneration executingmeans executes regeneration of the particulate filter by natural burningwithout activating the particulate filter regenerating means.
 12. Anexhaust gas purifying system according to claim 6, further comprising:anoxidization catalyst arranged upstream of the particulate filter forabsorbing nitrogen monoxide contained in the exhaust gas when theexhaust gas temperature is lower than 250° C. and for convertingnitrogen monoxide into nitrogen dioxide to release nitrogen monoxidewhen the exhaust gas temperature is between about 250° C. and 400° C.;wherein, when the exhaust gas temperature is between about 250° C. and400° C., the regeneration executing means executes regeneration of theparticulate filter by oxidizing particulate via the nitrogen dioxidewithout operating particulate filter regenerating means.
 13. An exhaustgas purifying system according to claim 1, further comprising:means forjudging whether the predicted running condition agrees with an actualrunning condition and whether the predicted exhaust gas property agreeswith an actual exhaust gas property; and means for re-predicting, whenthe agreement judging means judges that the predicted running conditiondoes not agree with the actual running condition, the future vehiclerunning condition and re-predicting the future exhaust gas propertybased on the re-predicted running condition.